Early work on OCT

During research on sensing between 1986-1995, the Applied Optics Group contributed towards several avenues which paved the way for the later development of what is known today as OCT.  We were involved in all three types of OCT;

  • Time domain OCT.
  • Spectral or Fourier domain OCT, where the interferometer output is sent to an optical spectrometer.
  • Swept source OCT, where a laser source is used which is swept within an equivalent band to that of the broadband source used in the time domain OCT or Fourier domain OCT.

A selection of papers published during that period:

En-face flying spot OCT

For en face OCT, we showed that there is no need for an external phase modulator if the object to be imaged is scattering and the image size is sufficiently large. The modulation is interestingly, created by scanning the beam over the target:

Then we moved the centre of the Newton rings out from the image centre and sampled the target with a grid of line:

This report demonstrates for the first time, B-scan OCT images from the retina constructed from T-scans (en-face 1D OCT scans):

The OCT/SLO (collaboration with Ophthalmic Technologies Inc.)

The research on flying spot en-face OCT showed us how to produce OCT images with the same orientation as that in microscopy, or in scanning laser ophthalmoscopy (SLO). This allowed us to devise and assemble a dual imaging system. The system outputs pairs of OCT and confocal images. Several ophthalmoogy groups are now using the OCT/SLO for imaging the eye.

Collaboration with New York Eye and Ear Infirmary and the Department of Ophthalmology Academic Medical Center, University of Amsterdam :

First OCT/ICG instrument for the eye, collaboration with New York Eye and Ear Infirmary:

Ultra high-resolution OCT/SLO system, collaboration with New York Eye and Ear Infirmary:

First OCT/SLO with AO correction, collaboration with National University of Ireland, Galway:

Sequential OCT/confocal. Sequential instead of simultaneous allows all signal to be used in each channel, OCT or confocal (SLO). (collaboration with New York Eye and Ear Infirmary):

Modulators and scanning methods for OCT

Using two RF modulators, we demonstrated simultaneous acquisition of two C-scans at two different depths:

Using a Mach Zehnder integrated modulator with independent RF excitation in each arm, we demonstrated simultaneous acquisition of two C-scans at two different depths, collaboration with University of Besancon:

Novel scanning delay line for fast A-scan but with less loss:

Using two coupled interferometers we devised a novel method for measuring the eye length:

  • A. Gh. Podoleanu, G. M. Dobre, D. J. Webb, and D. A. Jackson, “Fiberised set-up for Eye Length Measurement Full length,” Opt. Comm. 137, 397-405 (1997).

Corrections of distortions in OCT images

We make a distinction between scanning and refractive type distortions in OCT. This report also predicts a distorted elevation of the RPE layer in the fovea in the OCT images of the retina, due to differences in the indices of refraction of vitreous and retina (collaboration with University of Central Florida, School of Optics / CREOL and New York Eye and Ear Infirmary):

  • A. Podoleanu, I. Charalambous, L. Plesea,  A. Dogariu, and R. Rosen, “Correction of distortions in OCT imaging of the eye,” Phys. Med. Biol. 49, 1277-1294 (2004).

Signal to noise ratio analysis

Comparative noise analysis in the two channels of an OCT/SLO system:

  • A. Gh. Podoleanu, and D. A. Jackson, “Noise Analysis of a Combined Optical Coherence Tomograph and a Confocal Scanning Ophthalmoscope,” Appl. Opt. 38, 2116 – 2127 (1999).

This report shows that fast OCT systems have to work in the excess photon noise regime limitation and not in the shot noise regime:

Two novel noise bandwidth definitions are introduced to consider the excess photon noise in balanced OCT under wide bandwidth excitation:

Applications of OCT

OCT in ophthalmology

Posterior pole. The majority of reports above referred to examples in imaging the retina.  A novel method for topography using en-face OCT was presented in the following report (collaboration with Institute of Ophthalmology, London):

The utility of adjustable depth resolution required by en-face OCT method is presented in:

  • A. Gh. Podoleanu, J. A. Rogers, and D. A. Jackson, “OCT En-face Images from the Retina with Adjustable Depth Resolution in Real Time,” IEEE J. Select. Top. Quant. Electron. 5,  1176-1184 (1999).

Anterior pole:

  • A. Gh. Podoleanu, J. A. Rogers, G. M. Dobre, R. G. Cucu, and D. A. Jackson, “En-face OCT imaging of the anterior chamber,”  Proc. SPIE  4619, 240-243 (2002).

OCT in imaging skin

An OCT/SLO pair of a carried tooth

OCT in dentistry 

Collaboration with School of Dentistry, University of Liverpool:

  • B. T. Amaechi, S. M. Higham, A. Gh. Podoleanu, J. A. Rogers, and D. A. Jackson, “Use of optical coherence tomography for assessment of dental carries: quantitative procedure,” J. Oral Rehab. 28, 1092-1093 (2001).
  • B. T. Amaechi, A. Gh. Podoleanu, S.M. Higham, and D. Jackson, “Correlation of Quantitative Light-induced Fluorescence and Optical Coherence Tomography Applied for Detection and Quantification of Early Dental Caries,” J. Biomed. Opt. 8, 642-647 (2003).

OCT in imaging larynx and cochlea

Collaboration with Otolaryngology-Head & Neck Surgery Department, Guy’s Hospital, London:

  • A. G. Bibas, A. Gh. Podoleanu, R. G. Cucu, M. Bonmarin, G. M. Dobre, V. M. M Ward, E. Odell, A. Boxer, M. L Harries, M.J. Gleeson, “3-D Optical Coherence Tomography of the laryngeal mucosa,” Clinical Otolaryngology 29, 713-720 (2004).

OCT in imaging breast tissue

Collaboration with the Department of Histopathology, Imperial College School of Medicine, Hammersmith Hospital, London:

  • P. J. Tadrous, A. Gh. Podoleanu, S. Shousha, et al., “3D tissue imaging – A practical method using automated image registration and its application to the development of in vivo histological imaging techniques,” J. Pathology 195, 1A (2001).
  • P. J. Tadrous, A. Gh. Podoleanu, G. M. Dobre, G.W.H. Stamp Application of VRML for 3-dimensional, interactive, real-time comparison of OCT structures with standard histology,” Proc. SPIE 4956, 1605-7422 (2003).

Surface tomography of a hypervelocity impact crater.

Profilometry of craters using coherence radar

  • L. Kay, A. Gh. Podoleanu, M. Seeger, and C. J. Solomon, “A New Approach to the Measurement and Analysis of Impact Craters,” Int. J. Impact. Eng. 19, 739-753 (1997).

Imaging paintings

En-face OCT allows visualisation of under-drawings (Collaboration with the Nottingham Trent University, British Museum London and National Gallery, London). This was followed by a Leverhulme Grant.